U.S. patent number 10,568,700 [Application Number 15/193,524] was granted by the patent office on 2020-02-25 for catheter sensor systems.
This patent grant is currently assigned to INTUITIVE SURGICAL OPERATIONS, INC.. The grantee listed for this patent is INTUITIVE SURGICAL OPERATIONS, INC.. Invention is credited to Caitlin Q. Donhowe, Vincent Duindam, Giuseppe Maria Prisco.
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United States Patent |
10,568,700 |
Donhowe , et al. |
February 25, 2020 |
Catheter sensor systems
Abstract
A medical system comprises a catheter having a first section, a
second section and a main lumen extending through the first and
second sections. The system also includes an imaging probe sized to
extend through the main lumen of the catheter. The system also
includes a first electromagnetic sensor extending along a
longitudinal sensor axis at a proximal end of the first section and
a second electromagnetic sensor extending along the longitudinal
sensor axis at a distal end of the first section. The first section
between the proximal and distal ends flexibly couples the first and
second electromagnetic sensors so that the first electromagnetic
sensor is movable with respect to the second electromagnetic
sensor. The system also includes a third electromagnetic sensor
positioned on the imaging probe and a fiber shape sensor system
that extends through the first section between the proximal and
distal ends and along the first electromagnetic sensor and the
second electromagnetic sensor.
Inventors: |
Donhowe; Caitlin Q. (Mountain
View, CA), Duindam; Vincent (San Francisco, CA), Prisco;
Giuseppe Maria (Calci, IT) |
Applicant: |
Name |
City |
State |
Country |
Type |
INTUITIVE SURGICAL OPERATIONS, INC. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
INTUITIVE SURGICAL OPERATIONS,
INC. (Sunnyvale, CA)
|
Family
ID: |
48086482 |
Appl.
No.: |
15/193,524 |
Filed: |
June 27, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20160302873 A1 |
Oct 20, 2016 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13274237 |
Oct 14, 2011 |
9387048 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B
5/062 (20130101); A61M 25/0147 (20130101); A61B
34/10 (20160201); A61B 34/20 (20160201); A61M
25/0127 (20130101); A61B 2034/302 (20160201); A61B
2034/2061 (20160201); A61B 2034/2051 (20160201) |
Current International
Class: |
A61B
5/05 (20060101); A61B 34/20 (20160101); A61B
34/10 (20160101); A61B 5/06 (20060101); A61M
25/01 (20060101); A61B 34/30 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
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S57190549 |
|
Nov 1982 |
|
JP |
|
H06285009 |
|
Oct 1994 |
|
JP |
|
H07504363 |
|
May 1995 |
|
JP |
|
2000093522 |
|
Apr 2000 |
|
JP |
|
2000166936 |
|
Jun 2000 |
|
JP |
|
2003275223 |
|
Sep 2003 |
|
JP |
|
WO-9313916 |
|
Jul 1993 |
|
WO |
|
WO-9605768 |
|
Feb 1996 |
|
WO |
|
WO-9729690 |
|
Aug 1997 |
|
WO |
|
WO-0051486 |
|
Sep 2000 |
|
WO |
|
WO-0207809 |
|
Jan 2002 |
|
WO |
|
WO-2004016155 |
|
Feb 2004 |
|
WO |
|
WO-2005087128 |
|
Sep 2005 |
|
WO |
|
WO-2006039092 |
|
Apr 2006 |
|
WO |
|
WO-2007109418 |
|
Sep 2007 |
|
WO |
|
WO-2007146987 |
|
Dec 2007 |
|
WO |
|
WO-2008028149 |
|
Mar 2008 |
|
WO |
|
WO-2009002701 |
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Dec 2008 |
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WO |
|
Other References
Abbott, Daniel J. et al., "Design of an Endoluminal Notes Robotic
System," Conference on Intelligent Robots and Systems, 2007, pp.
410-416. cited by applicant .
Anisfield, Nancy; "Ascension Technology Puts Spotlight on DC Field
Magnetic Motion Tracking," HP Chronicle, Aug. 2000, vol. 17, No. 9,
3 Pages. cited by applicant .
Ascari, Luca et al., "A New Active Microendoscope for Exploring the
Sub-Arachnoid Space in the Spinal Cord," Proc. IEEE International
Conference on Robotics and Automation, 2003, pp. 2657-2662, vol. 2,
IEEE. cited by applicant .
Barnes Industries, Inc., "How a Ball Screw Works," 4 pages,
Copyright 2007; Internet: http://www.barnesballscrew.com/ball.htm.
cited by applicant .
Berthold III, John W., "Historical Review of Microbend Fiber-Optic
Sensors," Journal of Lightwave Technology, vol. 13, No. 7, Jul.
1995, pp. 1193-1199. cited by applicant .
Blue Road Research, "Overview of Fiber Optic Sensors," 40 pages,
first posted Dec. 8, 2004. Internet
<www.bluerr.com/papers/Overview_of_FOS2.pdf>. cited by
applicant .
Cao, Caroline G.L., "Designing Spatial Orientation in Endoscopic
Environments," Proceedings of the Human Factors and Ergonomics
Society 45th Annual Meeting, 2001, pp. 1259-1263. cited by
applicant .
Cao, Caroline G.L., "Disorientation in Minimal Access Surgery: A
Case Study," Proceedings of the IEA 2000/HFES 2000 Congress, pp.
4-169-4-172. cited by applicant .
Childers, Brooks A., et al., "Use of 3000 Bragg grating strain
sensors distributed on four eight-meter optical fibers during
static load tests of a composite structure," SPIE 8th International
Symposium on Smart Structures and Materials, Mar. 4-8, 2001,
Newport Beach, California, 10 Pages. cited by applicant .
Choi, Dong-Geol et al., "Design of a Spring Backbone Micro
Endoscope," Conference on Intelligent Robots and Systems, 2007, pp.
1815-1821. cited by applicant .
U.S. Appl. No. 11/762,185, filed Jun. 13, 2007. cited by applicant
.
U.S. Appl. No. 60/813,028, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,029, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,030, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,075, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,125, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,126, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,129, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,131, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,172, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,173, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,198, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,207, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 60/813,328, filed Jun. 13, 2006. cited by applicant
.
U.S. Appl. No. 61/334,978, filed May 14, 2010. cited by applicant
.
Cowie, Barbara M., et al., "Distributive Tactile Sensing Using
Fibre Bragg Grating Sensors for Biomedical Applications," 1st IEEE
/ RAS-EMBS International Conference on Biomedical Robotics and
Biomechatronics (BioRob 2006), Feb. 2006, pp. 312-317. cited by
applicant .
Danisch, Lee et al., "Spatially continuous six degree of freedom
position and orientation sensor," Sensor Review, 1999, vol. 19,
Issue 2, pp. 106-112. cited by applicant .
Dario, Paolo et al., "A Miniature Device for Medical Intracavitary
Intervention," Micro Electro Mechanical Systems '91 Proc IEEE `An
Investigation of Micro Structures, Sensors, Actuators, Machines and
Robots`, 1991, pp. 171-175, IEEE. cited by applicant .
Duncan, Roger, "Sensing Shape: Fiber-Bragg-grating sensor arrays
monitor shape at a high resolution," 2005, pp. 18-21, SPIE. cited
by applicant .
Extended European Search Report for Application No. EP20070798487,
dated Jan. 30, 2015, 8 pages. cited by applicant .
Gagarina, T. et al., "Modeling and experimental analysis of a new
bellow type actuators for active catheter end-effector," Proc. 10th
IEEE International Workshop on Robot and Human Interactive
Communication, 2001, pp. 612-617, IEEE. cited by applicant .
Gander, M.J. et al., "Bend measurement using Bragg gratings in
multicore fibre," Electronics Letter, Jan. 20, 2000, vol. 36, No.
2, 2 Pages. cited by applicant .
Hill, Kenneth O., "Fiber Bragg grating technology fundamentals and
overview," IEEE Journal of Lightwave Technology, vol. 15, Issue 8,
Aug. 1997, pp. 1263-1276. cited by applicant .
Ikuta, Koji et al., "Development of remote microsurgery robot and
new surgical procedure for deep and narrow space," Proc. IEEE
International Conference on Robotics & Automation, 2003, pp.
1103-1108, vol. 1, IEEE. cited by applicant .
Ikuta, Koji et al., "Shape memory alloy servo actuator system with
electric resistance feedback and application for active endoscope,"
Proc. IEEE International Conference on Robotics and Automation,
1988, pp. 427-430, vol. 1, IEEE. cited by applicant .
International Search Report and Written Opinion for Application No.
PCT/US2012/059889, dated Mar. 29, 2013, 14 pages. cited by
applicant .
International Search Report for application No. PCT/US07/71085,
dated Sep. 17, 2008, 2 pages. cited by applicant .
Jin, Long et al., "Two-dimensional bend sensing with a
cantilever-mounted FBG [Fiber Bragg Grating]," Meas. Sci. Technol.,
2006, pp. 168-172, vol. 17, Institute of Physics Publishing. cited
by applicant .
Kreger, Stephen et al., "Optical Frequency Domain Reflectometry for
High Density Multiplexing of Multi-Axis Fiber Bragg Gratings," 16th
International Conference on Optical Fiber Sensors (OFS-16), Oct.
2003, Nara, Japan, pp. 526-529. cited by applicant .
Lertpiriyasuwat, Vatchara et al., "Extended Kalman Filtering
Applied to a Two-Axis Robotic Arm with Flexible Links,"
International Journal of Robotics Research, 2000, vol. 19., No. 3,
pp. 254-270. cited by applicant .
Martinez, A. et al., "Vector Bending Sensors Based on Fibre Bragg
Gratings Inscribed by Infrared Femtosecond Laser," Electronics
Letters, 2005, pp. 472-474, vol. 41--Issue 8. cited by applicant
.
Measurand, "ShapeTape Overview," Measurand ShapeTape Advantage, pp.
1-3, first posted Nov. 3, 2004. Internet
<www.measurand.com/products/ShapeTape_overview.html>. cited
by applicant .
Meltz, Gerald, "Overview of Fiber Grating-Based Sensors,"
Proceedings of SPIE Distributed Multiplexed Fiber Optic Sensors VI,
Nov. 27, 1996, Eds. Kersey et al.,vol. 2838, pp. 2-22. cited by
applicant .
Office Action dated Jun. 17, 2014 for Japanese Application No.
20130179563 filed Aug. 30, 2013, 7 pages. cited by applicant .
Olympus Medical Systems, "Olympus ScopeGuide Receives FDA
Clearance," Press Release dated May 24, 2011, 2 pages. cited by
applicant .
Partial European Search Report for Application No. EP20120840613,
dated Jun. 5, 2015, 5 pages. cited by applicant .
PCT/US07/71085 Written Opinion, dated Sep. 17, 2008, 5 pages. cited
by applicant .
PCT/US09/46446 International Search Report and Written Opinion of
the International Searching Authority, dated Dec. 14, 2009, 21
pages. cited by applicant .
PCT/US09/46446 Partial International Search Report and Invitation
to Pay Additional Fees, dated Sep. 18, 2009, 9 pages. cited by
applicant .
PCT/US2011/035113 International Search Report and Written Opinion
of the International Searching Authority, dated Aug. 4, 2011, 13
pages. cited by applicant .
Shang, J. et al., "An Articulated Universal Joint Based Flexible
Access Robot for Minimally Invasive Surgery," 2011 IEEE Conference
on Robotics and Automation (ICRA), May 9-13, 2011, London, UK, pp.
1147-1152. cited by applicant .
Stieber, Michael E. et al., "Vision-Based Sensing and Control for
Space Robotics Applications," IEEE Transactions on Instrumentation
and Measurement, Aug. 1999, vol. 48, No. 4, pp. 807-812. cited by
applicant .
Sturges, Robert H. et al., "A Flexible, Tendon-Controlled Device
for Endoscopy," The International Journal of Robotics Research,
1993, pp. 121-131, vol. 12--Issue 2 , SAGE Publications. cited by
applicant .
Szewczyk, Jerome et al., "An active tubular polyarticulated
micro-system for flexible endoscope," Lecture Notes in Control and
Information Sciences, vol. 271, Experimental Robotics VII, 2000,
pp. 179-188, Springer-Verlag. cited by applicant .
Vertut, Jean and Phillipe Coiffet, Robot Technology: Teleoperation
and Robotics Evolution and Development, English translation,
Prentice-Hall, Inc., Inglewood Cliffs, NJ, USA 1986, vol. 3A, 332
pages. cited by applicant .
Wang, Yi-Ping et al., "A novel long period fiber grating sensor
measuring curvature and determining bend-direction simultaneously,"
IEEE Sensors Journal, 2005, pp. 839-843, vol. 5--Issue: 5, IEEE.
cited by applicant .
Webster, Robert J. III et al., "Toward Active Cannulas: Miniature
Snake-Like Surgical Robots," 2006, 7 pages. cited by applicant
.
Wong, Allan C. L. et al., "Multiplexed fibre Fizeau interferometer
and fibre Bragg grating sensor system for simultaneous measurement
of quasi-static strain and temperature using discrete wavelet
transform," Measurement Science and Technology, 2006, pp. 384-392,
vol. 17--Issue 2, Institute of Physics Publishing. cited by
applicant .
Zhang, Lunwei et al., "FBG Sensor Devices for Spatial Shape
Detection of Intelligent Colonoscope," IEEE International
Conference on Robotics and Automation, Apr. 2004, New Orleans,
Louisiana, pp. 835-840. cited by applicant.
|
Primary Examiner: Park; Patricia J
Attorney, Agent or Firm: Haynes and Boone, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser.
No. 13/274,237 (issued as U.S. Pat. No. 9,387,048), filed Oct. 14,
2011, which is incorporated herein by reference in its entirety.
This patent document is related to and incorporates by reference
the following co-filed patent applications: U.S. patent application
Ser. No. 13/274,198, filed Oct. 14, 2011, entitled "Catheters with
Control Modes for Interchangeable Probes"; U.S. patent application
Ser. No. 13/274,208 filed Oct. 14, 2011, entitled "Catheter with
Removable Vision Probe"; and U.S. patent application Ser. No.
13/274,229, filed Oct. 14, 2011, entitled "Vision Probe and
Catheter Systems."
Claims
What is claimed is:
1. A medical system comprising: a catheter having a first section,
a second section and a main lumen extending through the first and
second sections, the second section adjacent to the first section,
wherein the catheter defines a longitudinal catheter axis; an
imaging probe sized to extend through the main lumen of the
catheter; a first electromagnetic sensor extending along a
longitudinal sensor axis in parallel with the longitudinal catheter
axis at a proximal end of the first section, and a second
electromagnetic sensor extending along the longitudinal sensor axis
in parallel with the longitudinal catheter axis at a distal end of
the first section, the distal end of the first section being
adjacent to the second section, wherein the first section between
the proximal and distal ends flexibly couples the first and second
electromagnetic sensors so that the first electromagnetic sensor is
movable with respect to the second electromagnetic sensor, wherein
the first electromagnetic sensor includes a first signal wire
coupled to a first coil extending along the longitudinal sensor
axis and the second electromagnetic sensor includes a second signal
wire coupled to a second coil extending along the longitudinal
sensor axis; a third electromagnetic sensor positioned on the
imaging probe; and a fiber shape sensor system that extends through
the first section between the proximal and distal ends and along
the first electromagnetic sensor and the second electromagnetic
sensor, the fiber shape sensor system extending through the second
section, the fiber shape sensor system being configured for
measurement of a pose of the second section relative to the distal
end of the first section and measurement of a relative orientation
between the first electromagnetic sensor and the second
electromagnetic sensor.
2. The medical system of claim 1 wherein the imaging probe is
movable relative to the catheter.
3. The medical system of claim 1 wherein the second section is
steerable.
4. The medical system of claim 3 wherein the second section is
steerable via at least one actuation member extending through the
first section and into the second section.
5. The medical system of claim 1 further comprising a sheath
extending through the main lumen of the catheter and sized to
receive the imaging probe.
6. The medical system of claim 1, wherein the first electromagnetic
sensor is configured to measure a position and an orientation of
the proximal end of the first section relative to an external
reference.
7. The medical system of claim 6, wherein the second
electromagnetic sensor is configured to measure a position and an
orientation of the distal end of the first section relative to the
proximal end of the first section.
8. The medical system of claim 1, wherein the first electromagnetic
sensor and the second electromagnetic sensor are
five-degree-of-freedom sensors and wherein together, the first and
second electromagnetic sensors and the fiber shape sensor system
comprise a measurement system for determining a
six-degree-of-freedom measurement.
9. The medical system of claim 1, wherein the fiber shape sensor
system comprises fiber gratings.
10. The medical system of claim 1, wherein the first coil has a
first magnetic axis oriented at a first angle relative to the
longitudinal catheter axis; and the second coil has a second
magnetic axis that is oriented at a second angle relative to the
longitudinal catheter axis, the first and second angles being
different such that the second magnetic axis is askew from the
first magnetic axis.
11. The medical system of claim 1, wherein the fiber shape sensor
system is configured to measure a spatial relationship between the
first coil and the second coil.
12. A medical system comprising: a catheter having a first section,
a second section and a main lumen extending through the first and
second sections, the second section adjacent to the first section,
wherein the catheter defines a longitudinal catheter axis; an
imaging probe sized to extend through the main lumen of the
catheter; a first electromagnetic sensor extending along a
longitudinal sensor axis in parallel with the longitudinal catheter
axis at a proximal end of the first section, and a second
electromagnetic sensor extending along the longitudinal sensor axis
in parallel with the longitudinal catheter axis at a distal end of
the first section, the distal end of the first section being
adjacent to the second section, wherein the first section between
the proximal and distal ends flexibly couples the first and second
electromagnetic sensors so that the first electromagnetic sensor is
movable with respect to the second electromagnetic sensor, wherein
the first electromagnetic sensor includes a first signal wire
coupled to a first coil extending along the longitudinal sensor
axis and the second electromagnetic sensor includes a second signal
wire coupled to a second coil extending along the longitudinal
sensor axis; a third electromagnetic sensor positioned on the
imaging probe; a fiber shape sensor system that extends through the
first section between the proximal and distal ends and along the
first electromagnetic sensor and the second electromagnetic sensor,
the fiber shape sensor system extending through the second section,
the fiber shape sensor system being configured for measurement of a
pose of the second section relative to the distal end of the first
section and measurement of a relative orientation between the first
electromagnetic sensor and the second electromagnetic sensor; and
control logic that receives measurement information from the first
and second electromagnetic sensors and the fiber shape sensor
system and that generates a corrected actuator control signal based
on a desired configuration of the catheter and a measured shape of
a portion of the catheter extending between the proximal and distal
ends of the first section and based on the measurement of the
relative orientation between the first electromagnetic sensor and
the second electromagnetic sensor.
13. The medical system of claim 12, wherein the first
electromagnetic sensor includes a first coil that has a first
magnetic axis oriented at a first angle relative to the
longitudinal catheter axis; and the second electromagnetic sensor
includes a second coil has a second magnetic axis that is oriented
at a second angle relative to the longitudinal catheter axis, the
first and second angles being different such that the second
magnetic axis is askew from the first magnetic axis.
14. The medical system of claim 12 wherein the corrected actuator
control signal is used to steer least one actuation member
extending through the first section and into the second
section.
15. The medical system of claim 12, wherein the control logic
determines a six-degree-of-freedom measurement from a first
five-degree-of-freedom measurement from the first electromagnetic
sensor, a second five-degree-of-freedom measurement from the second
electromagnetic sensor, and a shape measurement from the fiber
shape sensor system.
Description
BACKGROUND
Medical devices that navigate body lumens need to be physically
small enough to fit within the lumens. Lung catheters, for example,
which may be used to perform minimally invasive lung biopsies or
other medical procedures, may need to follow airways that decrease
in size as the catheter navigates branching passages. To reach a
target location in a lung, a catheter may follow passages having
diameters as small as 3 mm or less. Manufacturing a catheter that
includes the mechanical and sensor structures suitable for remote
or robotic operation and that has a diameter that is sufficiently
small to navigate such small lumens can be challenging. In
particular, one desirable configuration for a remotely operated
catheter would provide a tool mounted on a steerable segment;
tendons or pull wires that extend down the length of the catheter
to an external drive system that pulls on the tendons to actuate
the tool or steerable segment; lumens for suction and/or
irrigation; a vision system for viewing of the target location; and
sensors to identify the location of the instrument relative to the
anatomy of a patient. Accommodating all of the desired features and
elements of a lung catheter or other device that is robotically
controlled and has a diameter about 3 mm or less can be
difficult.
SUMMARY
In accordance with an aspect of the invention, a robotic catheter
system using distal feedback can provide a small diameter for a
distal tip of the catheter and accurate measurements of the pose of
the distal tip through use of a sensor system including both
electromagnetic and fiber sensors. In accordance with an aspect of
the present invention, a sensor system for a catheter has a thicker
proximal section containing one or more electromagnetic (EM)
sensors and a thinner distal section containing a fiber shape
sensor. The EM sensor can provide an accurate measurement of a base
point of the distal section relative to the anatomy of a patient,
while the fiber sensor measures the shape of the distal section
extending from the base point. Accordingly, the distal section of
the catheter can be as small as a system using only a fiber shape
sensor, but the catheter system does not suffer from the inaccuracy
that is common to long fiber shape sensors.
One specific embodiment of the invention is a medical system
including a catheter, a first sensor system, and a second sensor
system. The catheter has a first section and a second section with
the second section being adjacent to the first section. The first
sensor system is in the first section and configured for
measurement of a pose of the first section. The second sensor
system is in the second section and configured for measurement of a
pose of the second section relative to the first section.
Another embodiment of the invention is a method for sensing a pose
of a distal tip of an elongated flexible structure such as a
catheter in a medical instrument. The method includes applying a
time-varying magnetic field to a space containing at least a
portion of the flexible structure. An electric signal induced in a
coil positioned at a location along the flexible structure of the
medical instrument can then be analyzed as part of the pose
measure. The location of the coil is separated from a proximal end
and the distal tip of the flexible structure. In addition to
analysis of the electrical signal from the coil, a shape of a
portion of the flexible structure that extends from the location of
the coil toward the distal end of the flexible section is
measured.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a robotic catheter system in accordance with an
embodiment of the invention having multiple control modes.
FIG. 2 shows an embodiment of a steerable segment that can be
employed in the system of FIG. 1.
FIGS. 3A and 3B show cross-sectional views of proximal and distal
sections of a catheter in accordance with an embodiment of the
invention.
FIG. 4 shows a cross-sectional view of a vision probe that may be
deployed in the catheter of FIGS. 3A and 3B and swapped out for use
of medical probes in the catheter shown in FIGS. 3A and 3B.
FIG. 5 is a flow diagram of a process for using the catheter system
with a removable vision system and multiple control modes.
FIG. 6 is a flow diagram of a catheter control process in a holding
mode.
FIG. 7 shows sensing coils that can be employed in electromagnetic
sensors in medical systems in some embodiments of the
invention.
FIGS. 8A, 8B, 8C, and 8D illustrate alternative configurations for
sensor systems in accordance with embodiments of the invention
including electromagnetic and shape sensors.
FIG. 9 shows cross-sections of a catheter system containing a
six-degree-of-freedom EM sensor and a catheter system containing
two five-degree-of-freedom EM sensors.
Use of the same reference symbols in different figures indicates
similar or identical items.
DETAILED DESCRIPTION
A robotic catheter for use in small lumens such as airways and
passages in the respiratory tract employs combinations of one or
more EM sensors and a fiber shape sensor to provide accurate
measurements of the pose of a small-diameter distal tip. FIG. 1
schematically illustrates a catheter system 100 in accordance with
one embodiment of the invention. In the illustrated embodiment,
catheter system 100 includes a catheter 110, a drive interface 120,
control logic 140, an operator interface 150, and a sensor system
160.
Catheter 110 is a generally flexible device having one or more
lumens including a main lumen that can accommodate interchangeable
probes such as described further below. Flexible catheters can be
made using a braided structure such as a woven wire tube with inner
or outer layers of a flexible or low friction material such as
polytetrafluoroethylene (PTFE). In one embodiment, catheter 110
includes a bundle of lumens or tubes held together by a braided
jacket and a reflowed (i.e., fused by melting) jacket of a material
such as Polyether Block Amide (Pebax). Alternatively, an extrusion
of a material such as Pebax can similarly be used to form multiple
lumens in catheter 110. Catheter 110 particularly includes a main
lumen for interchangeable probe systems and smaller lumens for pull
wires and sensor lines. In the illustrated embodiment, catheter 110
has a proximal section 112 attached to drive interface 120 and a
distal section 114 that extends from the proximal section 112. An
additional steerable segment 116 (e.g., a metal structure such as
shown in FIG. 2 and described further below) can form the distal
subsection of distal section 114. Pull wires extend from drive
system 120 through proximal section 112 and distal section 114 and
connect to steerable segment 116.
The overall length of catheter 110 may be about 60 to 80 cm or
longer with distal section 114 being about 15 cm long and steerable
segment 116 being about 4 to 5 cm long. In accordance with an
aspect of the invention, distal section 114 has a smaller diameter
than does proximal section 112 and thus can navigate smaller
natural lumens or passages. During a medical procedure, at least a
portion of proximal section 112 and all of distal section 114 may
be inserted along a natural lumen such as an airway of a patient.
The smaller diameter of distal section 114 permits use of distal
section 114 in lumens that may be too small for proximal section
112, but the larger diameter of distal section 114 facilitates
inclusion of more or larger structures or devices such as
electromagnetic (EM) sensors 162 that may not fit in distal section
114.
Steerable segment 116 is remotely controllable and particularly has
a pitch and a yaw that can be controlled using pull wires.
Steerable segment 116 may include all or part of distal section 114
and may be simply implemented as a multi-lumen tube of flexible
material such as Pebax. In general, steerable segment 116 is more
flexible than the remainder of catheter 110, which assists in
isolating actuation or bending to steerable segment 116 when drive
interface 120 pulls on actuating tendons. Catheter 110 can also
employ additional features or structures such as use of Bowden
cables for actuating tendons to prevent actuation from bending
proximal section 112 (or bending any portion the section of 114
other than steerable segment 116) of catheter 110. FIG. 2 shows one
specific embodiment in which steerable segment 116 is made from a
tube 210 that in catheter 110 of FIG. 1 contains multiple tubes
defining a main lumen for a probe system and smaller lumens for
actuation tendons 230 and a shape sensor not shown in FIG. 2. In
the illustrated embodiment, tendons 230 are placed 90.degree. apart
surrounding lumen 312 to facilitate steering catheter 110 in pitch
and yaw directions defined by the locations of tendons 230. A
reflowed jacket, which is not shown in FIG. 2 to better illustrate
the internal structure of steerable segment 116, may also cover
tube 210. As shown in FIG. 2, tube 210 is cut or formed to create a
series of flexures 220. Tendons 230 connect to a distal tip 215 of
steerable segment 116 and extend back to a drive interface 120.
Tendons 230 can be coated or uncoated, single filament or multi
strand wires, cables, Bowden cables, hypotubes, or any other
structures that are able to transfer force from drive interface 120
to distal tip 215 and limit bending of proximal section 112 when
drive interface 120 pulls on tendons 230. Tendons 230 can be made
of any material of sufficient strength including but not limited to
a metal such as steel or a polymer such as Kevlar. In operation,
pulling harder on any one of tendons 230 tends to cause steerable
segment 116 to bend in the direction of that tendon 230. To
accommodate repeated bending, tube 210 may be made of a material
such as Nitinol, which is a metal alloy that can be repeatedly bent
with little or no damage.
Drive interfaces 120 of FIG. 1, which pulls on tendons 230 to
actuate steerable segment 116, includes a mechanical system or
transmission 124 that converts the movement of actuators 122, e.g.,
electric motors, into movements of (or tensions in) tendons 230
that run through catheter 110 and connect to steerable segment 116.
(Push rods could conceivably be used in catheter 110 instead of
tendons 230 but may not provide a desirable level of flexibility.)
The movement and pose of steerable segment 116 can thus be
controlled through selection of drive signals for actuators 122 in
drive interface 120. In addition to manipulating tendons 230, drive
interface 120 may also be able to control other movement of
catheter 110 such as range of motion in an insertion direction and
rotation or roll of the proximal end of catheter 110, which may
also be powered through actuators 122 and transmission 124. Backend
mechanisms or transmissions that are known for flexible-shaft
instruments could in general be used or modified for drive
interface 120. For example, some known drive systems for flexible
instruments are described in U.S. Pat. App. Pub. No. 2010/0331820,
entitled "Compliant Surgical Device," which is hereby incorporated
by reference in its entirety. Drive interface 120 in addition to
actuating catheter 110 should allow removal and replacements of
probes in catheter 110, so that the drive structure should be out
of the way during such operations.
A dock 126 in drive interface 120 can provide a mechanical coupling
between drive interface 120 and catheter 110 and link actuation
tendons 230 to transmission 124. Dock 126 may additionally contain
an electronic or optical system for receiving, converting, and/or
relaying sensor signals from portions of sensor system 160 in
catheter 110 and contain an electronic or mechanical system for
identifying the probe or the type of probe deployed in catheter
110.
Control logic 140 controls the actuators in drive interface 120 to
selectively pull on the tendons as needed to actuate and steer
steerable segment 116. In general, control logic 140 operates in
response to commands from a user, e.g., a surgeon or other medical
personnel using operator interface 150, and in response to
measurement signals from sensor system 160. However, in holding
modes as described further below, control logic 140 operates in
response to measurement signals from sensor system 160 to maintain
or acquire a previously identified working configuration. Control
logic 140 may be implemented using a general purpose computer with
suitable software, firmware, and/or interface hardware to interpret
signals from operator interface 150 and sensor system 160 and to
generate control signals for drive interface 120.
In the illustrated embodiment, control logic 140 includes multiple
modules 141, 142, 143, and 144 that implement different processes
for controlling the actuation of catheter 110. In particular,
modules 141, 142, 143, and 144 respectively implement a position
stiffening mode, an orientation stiffening mode, a target position
mode, and a target axial mode, which are described further below. A
module 146 selects which control process will be used and may base
the selection on user input, the type or status of the probe
deployed in catheter 110, and the task being performed. Control
logic 140 also includes memory storing parameters 148 of a working
configuration of steerable segment 116 that is desired for a task,
and each of the modules 141, 142, 143, and 144 can use their
different control processes to actively maintain or hold the
desired working configuration.
Operator interface 150 may include standard input/output hardware
such as a display, a keyboard, a mouse, a joystick, or other
pointing device or similar I/O hardware that may be customized or
optimized for a surgical environment. In general, operator
interface 150 provides information to the user and receives
instructions from the user. For example, operator interface 150 may
indicate the status of system 100 and provide the user with data
including images and measurements made by system 100. One type of
instruction that the user may provide through operator interface
150, e.g., using a joystick or similar controller, indicates the
desired movement or position of steerable segment 116, and using
such input, control logic 140 can generate control signals for
actuators in drive interface 120. Other instructions from the user
can, for example, select an operating mode of control logic
140.
Sensor system 160 generally measures a pose of steerable segment
116. In the illustrated embodiment, sensor system 160 includes EM
sensors 162 and a shape sensor 164. EM sensors 162 include one or
more conductive coils that may be subjected to an externally
generated electromagnetic field. Each coil of EM sensors 162 then
produces an induced electrical signal having characteristics that
depend on the position and orientation of the coil relative to the
externally generated electromagnetic field. In an exemplary
embodiment, EM sensors 162 are configured and positioned to measure
six degrees of freedom, e.g., three position coordinates X, Y, and
Z and three orientation angles indicating pitch, yaw, and roll of a
base point. The base point in system 100 is at or near the end of
proximal section 112 and the start of distal section 114 of
catheter 110. Shape sensor 164 in the exemplary embodiment of the
invention includes a fiber grating that permits determination of
the shape of a portion of catheter 110 extending from the base
point, e.g., the shape of distal section 114 or steerable segment
116. Such shape sensors using fiber gratings are further described
in U.S. Pat. No. 7,720,322, entitled "Fiber Optic Shape Sensor,"
which is hereby incorporated by reference in its entirety. An
advantage of the illustrated type of sensor system 160 is that EM
sensors 162 can provide measurements relative to the externally
generated magnetic field, which can be calibrated relative to a
patient's body. Thus, system 160 can use EM sensors 162 to reliably
measure the position and orientation of a base point for shape
sensor 164, and shape sensor 164 need only provide shape
measurement for a relatively short distance. Additionally, distal
section 114 only contains shape sensor 164 and may have a diameter
that is smaller than the diameter of proximal section 112. More
generally, sensor system 160 need only be able to measure the pose
of steerable segment 116, and other types of sensors could be
employed.
FIGS. 3A and 3B respectively show cross-sections of the proximal
and distal sections 112 and 114 of catheter 110 in one embodiment
of the invention. FIG. 3A shows an embodiment of catheter 110
having a body 310 that includes a main lumen 312 for a vision or
medical probe, lumens 314 containing tendons 230, lumens 316
containing EM sensors 162 or associated signal wires, and a lumen
318 containing a fiber shape sensor 164. Main lumen 312, tendon
lumens 314, and a shape sensor lumen 318 extend into distal section
114 as shown in FIG. 3B, but lumens 316 for EM sensors 162 are not
needed in distal section 114 because EM sensors 162 are only in
proximal section 112. Accordingly, distal section 114 can be
smaller than proximal section 112 particularly because the lumen
318 for fiber shape sensor 164 fits between two lumens 314 for pull
wires and does not negatively affect the outside diameter of distal
section 114. In an exemplary embodiment, body 310 in proximal
section 112 has an outer diameter of about 4 mm (e.g., in a range
from 3 to 6 mm) and provides main lumen 312 with a diameter of
about 2 mm (e.g., in a range from 1 to 3 mm) and in distal section
114 has an outer diameter of about 3 mm (e.g., in a range from 2 to
4 mm) while maintaining the diameter of main lumen 312 at about 2
mm. A smooth taper (as shown in FIG. 1) or an abrupt step in body
310 can be used at the transition from the larger diameter of
proximal section 112 to the smaller diameter of distal section
114.
The specific dimensions described in above are primarily for a
catheter that accommodates probes having a diameter of 2 mm, which
is a standard size for existing medical tools such as lung biopsy
probes. However, alternative embodiments of the invention could be
made larger or smaller to accommodate medical probes with a larger
or smaller diameter, e.g., 1 mm diameter probes. A particular
advantage of such embodiments is that a high level of functionality
is provided in a catheter with relative small outer diameter when
compared to the size of probe used in the catheter.
FIGS. 3A and 3B also show a sheath 360 that may be employed between
catheter body 310 and a probe in main lumen 312. In one embodiment
of catheter 110, sheath 360 is movable relative to body 310 and can
be extended beyond the end of steerable segment 116. This may be
advantageous in some medical procedures because sheath 360 is even
smaller than distal section 114 and therefore may fit into smaller
natural lumens or passages. For example, if catheter 110 reaches a
branching of lumens that are too small to accommodate steerable
segment 116, steerable segment 116 may be pointed in the direction
of the desired branch, so that sheath 360 can be pushed beyond the
end of steerable segment 116 and into that branch. Sheath 360 could
thus reliably guide a medical probe into the desired branch.
However, sheath 360 is passive in that it is not directly actuated
or steerable. In contrast, distal section 114 accommodates
actuation tendons 230 that connect to steerable segment 116 and can
be manipulated to steer or pose steerable segment 116. In some
medical applications, the active control of steerable segment 116
is desirable or necessary during a medical procedure, and passive
sheath 360 may not be used in some embodiments of the
invention.
Main lumen 312 is sized to accommodate a variety of medical probes.
One specific probe is a vision probe 400 such as illustrated in
FIG. 4. Vision probe 400 has a flexible body 410 with an outer
diameter (e.g., about 2 mm) that fits within the main lumen of
catheter 110 and with multiple inner lumens that contain the
structures of vision probe 400. Body 410 may be formed using an
extruded flexible material such as Pebax or another polymer, which
allows creation of multiple lumens and thin walls for maximal
utility in minimal cross-sectional area. A multi-lumen extrusion
also neatly organizes the location of the components. The length of
body 410 may optionally include a combination of two multi-lumen
extrusions, for example, a distal extrusion "butt-welded" to a
proximal extrusion. This may be done, for example, so that the
proximal or distal extrusion has desired shape, e.g., a clover-leaf
or oval outside shape, to mate with a complementary keying feature
in catheter 110. These mating shapes or keying structures can
prevent the probe from rotating within the catheter and assure a
known orientation of camera 320 relative to catheter 110.
In the illustrated embodiment, the structure of vision probe 400
includes a CMOS camera 420, which is at the distal end of the probe
and connected through one or more signal wires (not shown) that
extend along the length of vision probe 400, e.g., to provide a
video signal to control logic 140 or operator interface 150 as
shown in FIG. 1. Alternatively, a fiber bundle imaging system could
be employed, but CMOS cameras 420 can typically provide images of
higher quality than can be achieved with fiber bundle imaging
systems. Vision probe 400 also includes illumination fibers 430
that surround camera 420 and provide light for imaging within a
body lumen. In an exemplary embodiment, illumination fibers 430 are
made of a flexible material such as plastic, which tends to be more
flexible than glass fibers. Oblong fluid ports 440 are provided in
body 410 for suction and irrigation that may be useful, for
example, for rinsing of a lens of camera 420. Fluid ports 440 can
also be used for delivering drugs, e.g., for numbing, before vision
probe 400 is removed from catheter 110 and replaced with a biopsy
probe. Although the illustrated embodiment of vision probe 400
includes multiple fluid ports 440, a single fluid port could be
used for both irrigation and suction, and vision probe 400 could
alternatively have only a single fluid port to save space. Vision
probe 400 may additionally include an electromagnetic sensor (not
shown) embedded just proximally to CMOS camera 420 to provide
additional pose information about the tip of vision probe 400.
Vision probe 400 is adapted to be inserted or removed from catheter
110 while catheter 110 is in use for a medical procedure.
Accordingly, vision probe 400 is generally free to move relative to
catheter 110. While movement relative to catheter 110 is necessary
or desirable during insertion or removal of vision probe 400, the
orientation of a vision probe 400 (and some medical probes) may
need to be known for optimal or easier use. For example, a user
viewing video from vision probe 400 and operating a controller
similar to a joystick to steer catheter 110 generally expects the
directions of movement of the controller to correspond to the
response of steerable segment 116 and the resulting change in the
image from vision probe 400. Operator interface 150 needs (or at
least can use) information on the orientation of vision probe 400
relative to tendons 230 in order to provide a consistency in
directions used in the user interface. In accordance with an aspect
of the invention, a keying system (not shown) can fix vision probe
400 into a known orientation relative to catheter 110 and tendons
230. The keying system may, for example, be implemented through the
shape of a proximal or distal section of probe 400 or include a
spring, fixed protrusion, or latch on vision probe 400 or steerable
segment 116 and a complementary notch or feature in steerable
segment 116 or vision probe 400.
Vision probe 400 is only one example of a probe system that may be
deployed in catheter 110 or guided through catheter 110 to a work
site. Other probe systems that may be used include, but are not
limited to, biopsy forceps, biopsy needles, biopsy brushes,
ablation lasers, and radial ultrasound probes. In general, catheter
110 can be used with existing manual medical probes that are
commercially available from medical companies such as Olympus
Europa Holding GmbH.
The catheter system 100 of FIG. 1 can be used in procedures that
swap a vision probe and a medical probe. FIG. 5 is a flow diagram
of one embodiment of a process 500 for using the catheter system
100 of FIG. 1. In process 500, vision probe 400 is deployed in
catheter 110 in step 510, and catheter 110 is inserted along a path
including a natural lumen of a patient. For example, for a lung
biopsy, steerable segment 116 of catheter 110 may be introduced
through the mouth of a patient into the respiratory tract of the
patient. Vision probe 400 when fully deployed in catheter 110 may
fit into a keying structure that keeps vision probe 400 in a
desired orientation at or even extending beyond steerable segment
116 to provide a good forward view from steerable segment 116 of
catheter 110. As noted above, steerable segment 116 of catheter 110
is steerable, and vision probe 320 can provide video of the
respiratory tract that helps a user when navigating catheter 110
toward a target work site. However, use of vision probe 400 during
navigation is not strictly necessary since navigation of catheter
110 may be possible using measurements of sensor system 160 or some
other system with or without vision probe 400 being deployed or
used in catheter 110. The path followed to the work site may be
entirely within natural lumens such as the airways of the
respiratory track or may pierce and pass through tissue at one or
more points.
When steerable segment 116 reaches the target work site, vision
probe 400 can be used to view the work site as in step 530 and to
pose steerable segment 116 for performance of a task at the target
work site as in step 540. Posing of steerable segment 116 may use
images or visual information from vision probe 400 and measurements
from sensor system 160 to characterize the work site and determine
the desired working configuration. The desired working
configuration may also depend on the type of tool that will be used
or the next medical task. For example, reaching a desired working
configuration of catheter 110 may bring the distal tip of steerable
segment 116 into contact with tissue to be treated, sampled, or
removed with a medical tool that replaces vision probe 400 in
catheter 110. Another type of working configuration may point
steerable segment 116 at target tissue to be removed using an
ablation laser. For example, tissue could be targeted in one or
more 2D camera views while vision probe 400 is still in place in
catheter 110, or target tissue can be located on a virtual view of
the work site using pre-operative 3D imaging data together with the
position sensing relative to patient anatomy. Still another type of
working configuration may define a line for the insertion of a
needle or other medical tool into tissue, and the working
configuration includes poses in which the distal tip of steerable
segment 116 is along the target line. In general, the desired
working configuration defines constraints on the position or the
orientation of the distal tip of steerable segment 116, and the
shape of more proximal sections of catheter 110 is not similarly
constrained and may vary as necessary to accommodate the
patient.
Step 550 stores in memory of the control logic parameters that
identify the desired working configuration. For example, the
position of a distal tip or target tissue can be defined using
three coordinates. A target line for a need can be defined using
the coordinates of a point on the line and angles indicating the
direction of the line from that point. In general, control logic
120 uses the stored parameters that define the desired working
configuration when operating in a holding mode that maintains
steerable segment 116 of catheter 110 in the desired working
configuration as described further below.
Step 560 selects and activates a holding mode of the catheter
system after the desired working configuration has been established
and recorded. Control logic 140 for catheter 110 of FIG. 1 may have
one or more modules 141, 142, 143, and 144 implementing multiple
stiffening modes that may be used as holding modes when the desired
configuration of steerable segment 116 has fixed constraints. The
available control modes may include one or more of the
following.
1.) A position stiffness mode compares the position of the distal
tip of steerable segment 116 as measured by sensor system 160 to a
desired tip position and controls the actuators to minimize the
difference in desired and measured tip positions. The position
stiffness mode may particularly be suitable for general
manipulation tasks in which the user tries to precisely control the
position of the tip and for situations where the distal tip
contacts tissue.
2.) An orientation stiffness mode compares the measured orientation
or pointing direction of the distal tip to a desired pointing
direction of the distal tip and controls the actuators to minimize
the difference in desired and actual tip pointing direction. This
orientation stiffening that may be suitable, e.g., when controlling
an imaging device such as vision probe 400 attached steerable
segment 116, in which case the viewing direction is kept as
desired, while the exact position of steerable segment 116 may be
less important.
3.) A target position stiffness mode uses a combination of the
measured tip position and pointing direction to control catheter
110 to always point the distal tip of steerable segment 116 towards
a specified target point some distance in front of steerable
segment 116. In case of external disturbances, control logic 140
may control the actuators to implement this target position
stiffening behavior, which may be suitable, e.g., when a medical
probe inserted though the catheter contains an ablation laser that
should always be aimed at a target ablation point in tissue.
4.) A target axial motion stiffness mode uses a combination of the
measured tip position and pointing direction to ensure that the
distal tip of steerable segment 116 is always on a line in space
and has a pointing direction that is also along that line. This
mode can be useful, e.g., when inserting a biopsy needle along a
specified line into tissue. Tissue reaction forces could cause the
flexible section of catheter 110 to bend while inserting the
needle, but this control strategy would ensure that the needle is
always along the right line.
The selection of a mode in step 560 could be made through manual
selection by the user, based on the type of probe that is being
used (e.g., grasper, camera, laser, or needle) in catheter 110, or
based on the activity catheter 110 is performing. For example, when
a laser is deployed in catheter 110, control logic 120 may operate
in position stiffness mode when the laser deployed in catheter 110
is off and operate in target position stiffness mode to focus the
laser on a desired target when the laser is on. When "holding" is
activated, control logic 140 uses the stored parameters of the
working configuration (instead of immediate input from operator
interface 150) in generating control signals for drive interface
120.
The vision probe is removed from the catheter in step 570, which
clears the main lumen of catheter 110 for the step 580 of inserting
a medical probe or tool through catheter 110. For the specific step
order shown in FIG. 5, control logic 140 operates in holding mode
and maintains steerable segment 116 in the desired working
configuration while the vision system is removed (step 570) and the
medical probe is inserted (step 580). Accordingly, when the medical
probe is fully deployed, e.g., reaches the end of steerable segment
116, the medical probe will be in the desired working
configuration, and performance of the medical task as in step 590
can be then performed without further need or use of the removed
vision probe. Once the medical task is completed, the catheter can
be taken out of holding mode or otherwise relaxed so that the
medical probe can be removed. The catheter can then be removed from
the patient if the medical procedure is complete, or the vision or
another probe can be inserted through the catheter if further
medical tasks are desired.
In one alternative for the step order of process 500, catheter 110
may not be in a holding mode while the medical probe is inserted
but can be switched to holding mode after the medical probe is
fully deployed. For example, catheter 110 may be relaxed or
straightened for easy remove of vision probe 400 (step 570) and
insertion of the medical probe (step 580). Once holding mode is
initiated, e.g., after insertion of the medical probe, control
logic 140 will control the drive interface 130 to return steerable
segment 116 to the desired working configuration if steerable
segment 116 has moved since being posed in the desired working
configuration. Thereafter, control logic 140 monitors the pose of
steerable segment 116 and actively maintains steerable segment 116
in the desired working configuration while the medical task is
performed in step 590.
FIG. 6 shows a flow diagram of a process 600 of a holding mode that
can be implemented in control logic 140 of FIG. 1. Process 600
begins in step 610 with receipt of measurement signals from sensor
system 160. The particular measurements required depend on the type
of holding mode being implemented, but as an example, the
measurements can indicate position coordinates, e.g., rectangular
coordinates X, Y, and Z, of the distal tip of steerable segment 116
and orientation angles, e.g., angles .theta..sub.X, .theta..sub.Y,
and .theta..sub.Z of a center axis of the distal tip of steerable
segment 116 relative to coordinate axes X, Y, and Z. Other
coordinate systems and methods for representing the pose of
steerable segment 116 could be used, and measurements of all
coordinates and direction angles may not be necessary. However, in
an exemplary embodiment, sensor system 160 is capable of measuring
six degrees of freedom (DoF) of the distal tip of steerable segment
116 and of providing those measurements to control logic 140 in
step 610.
Control logic 140 in step 620 determines a desired pose of
steerable segment 116. For example, control logic 140 can determine
desired position coordinates, e.g., X', Y', and Z', of the end of
steerable segment 116 and desired orientation angles, e.g., angles
.theta.'.sub.X, .theta.'.sub.Y, and .theta.'.sub.Z of the center
axis of steerable segment 116 relative to coordinate axes X, Y, and
Z. The holding modes described above generally provide fewer than
six constraints on the desired coordinates. For example, position
stiffness operates to constrain three degrees of freedom, the
position of the end of steerable segment 116 but not the
orientation angles. In contrast, orientation stiffness mode
constrains one or more orientation angles but not the position of
end of steerable segment 116. Target position stiffness mode
constrains four degrees of freedom, and axial stiffness mode
constrains five degrees of freedom. Control logic 610 can impose
further constraints to select one of set of parameters, e.g., X',
Y', and Z' and angles .theta.'.sub.X, .theta.'.sub.Y, and
.theta.'.sub.Z, that provides the desired working configuration.
Such further constraints include but are not limited to mechanical
constraints required by the capabilities of steerable segment 116
and of catheter 110 generally and utilitarian constraints such as
minimizing movement of steerable segment 116 or providing desired
operating characteristics such as smooth, non-oscillating, and
predictable movement with controlled stress in catheter 110. Step
620 possibly includes just keeping a set pose steerable segment 116
by finding smallest movement from the measured pose to a pose
satisfying the constraints, e.g., finding the point on the target
line closest to the measure position for axial motion stiffness or
finding some suitable pose from registered pre-op data that is
close to the current pose.
Control logic 140 in step 630 uses the desired and/or measured
poses to determine corrected control signals that will cause drive
interface 120 to move steerable segment 116 to the desired pose.
For example, the mechanics of catheter 110 and drive interface 120
may permit development of mappings from the desired coordinates X',
Y', and Z' and angles .theta.'.sub.X, .theta.'.sub.Y, and
.theta.'.sub.Z to actuator control signals that provide the desired
pose. Other embodiments may use differences between the measured
and desired pose to determine corrected control signals. In
general, the control signals may be used not only to control
actuators connected through tendons to steerable segment 116 but
may also control (to some degree) insertion or roll of catheter 110
as a whole.
A branch step 650 completes a feedback loop by causing process 600
to return to measurement step 610 after control system 140 applies
new control signals drive interface 120. The pose of distal tip is
thus actively monitored and controlled according to fixed
constraints as long as control system 120 remains in the holding
mode. It may be noted, however, that some degrees of freedom of
steerable segment 116 may not require active control. For example,
in orientation stiffness mode, feedback control could actively
maintain pitch and yaw of steerable segment 116, while the
mechanical torsional stiffness of catheter 110 is relied on hold
the roll angle fixed. However, catheter 110 in general may be
subject to unpredictable external forces or patient movement that
would otherwise cause catheter 110 to move relative to the work
site, and active control as in process 600 is needed to maintain or
hold the desired working configuration.
The sensor system 160 of a catheter 100 as noted above can employ
both an EM sensor 162 and a fiber shape sensor 164. EM sensors or
trackers are state-of-the-art position and orientation sensors that
combine high global accuracy with small package size (e.g., about
1.times.10 mm). EM sensors are commercially available from
companies such as Ascension Technology Corporation and Northern
Digital Inc. Shape sensing technology, which may be used in the
above described embodiments, commonly employ reflections and
interference within an optical fiber to measure the shape along the
length of the optical fiber. This shape sensing technology is good
for giving 6-DoF relative measurements between two points along the
fiber as well as measuring bend angles of controllable joints or
providing full three-dimensional shape information. A typical fiber
shape sensor of this type may have a diameter of about 0.2 mm,
which is considerably smaller than a typical EM sensor.
FIG. 7 illustrates three different types of sensing coils 710, 720,
and 730 that could be used in an EM sensor. In operation, the
sensing coil, e.g., coil 710, in the catheter or other device is
placed in a well-controlled magnetic field that an external EM
generator produces. The EM generator typically has the form of a
square or cylindrical box of 20-60 cm wide and several cm thick and
may have a fixed position relative to the patient. The magnetic
field produced by the generator varies in time and induces a
voltage and electric current in the sensing coil 710. U.S. Pat. No.
7,197,354, entitled "System for Determining the Position and
Orientation of a Catheter"; U.S. Pat. No. 6,833,814, entitled
"Intrabody Navigation System for Medical Applications"; and U.S.
Pat. No. 6,188,355, entitled "Wireless Six-Degree-of-Freedom
Locator" describe the operation of some EM sensor systems suitable
for in medical environment and are hereby incorporated by reference
in their entirety. U.S. Pat. No. 7,398,116, entitled "Methods,
Apparatuses, and Systems useful in Conducting Image Guided
Interventions," U.S. Pat. No. 7,920,909, entitled "Apparatus and
Method for Automatic Image Guided Accuracy Verification," U.S. Pat.
No. 7,853,307, entitled "Methods, Apparatuses, and Systems Useful
in Conducting Image Guided Interventions," and U.S. Pat. No.
7,962,193, entitled "Apparatus and Method for Image Guided Accuracy
Verification" further describe systems and methods that can use
electromagnetic sensing coils in guiding medical procedures and are
also incorporated by reference in their entirety. In general, the
induced voltage in a sensing coil depends on time derivative the
magnetic flux, which in turn depends on the strength of the
magnetic field and the direction of the magnetic field relative to
a normal to the areas of loops in the coil. The field generator can
vary the direction and magnitude of the magnetic field in a
systematic manner that enables at least partial determination of
the pose of coil 710 from the induced electric signal. Up to five
degrees of freedom can be determined using a sensor 162 containing
a single sensing coil 710. However, sensing coil 710 is
cylindrically symmetric, so that a roll angle, i.e., an angle
indicating orientation about a normal 712 to the inductive areas of
coil 710, cannot be determined. Only the position and the pointing
direction can be determined using a single coil 710. Even so, a
5-Degree-of-Freedom (5-DoF) sensor containing a single sensing coil
710 is useful in many medical systems. In particular, the
mechanical shape of a typical sensing coil (long and slender) fits
well with the mechanical shape of minimally invasive medical tools,
and if the tool is rotationally symmetrical (e.g. in the case of a
needle or laser fiber), the roll angle is not relevant.
A robotic control catheter such as catheter 110 may need a 6-DoF
measurement including a measurement of the roll angle so that the
positions of actuating tendons are known. If measurement of the
roll angle is of interest, two 5-DoF EM sensors can be combined to
create a 6-DoF EM sensor. One specific configuration of a 6-DoF EM
sensor uses two coils such as 710 with the inductive areas of two
coils having normal vectors that are askew, e.g., perpendicular to
each other. More generally, the two coils need to be arranged so
that the normal vectors to inductive areas are not along the same
axis, and larger angles between the normal vectors generally
provide better measurement accuracy. Coils 720 and 730 illustrate
how a coil 720 or 730 that may have wire loops with a normal 722 or
732 that is at a non-zero angle to the axes of a cylinder
containing the coil 720 or 730. Coils 720 and 730 can thus be
oriented along the same direction, e.g., along the length of a
catheter or other medical tool, and still be used to measure six
degrees of freedom.
FIG. 8A shows a configuration of a catheter system 810 having a
proximal section 812 containing a 6-DoF EM sensor 820 and a distal
section 814 containing a fiber shape sensor 822. EM sensor 820
terminates at or near a distal end of proximal section 812.
Accordingly, distal section 814 can have a diameter (e.g., about 3
mm to accommodate a probe diameter of about 2 mm) that is smaller
than the diameter (e.g., about 4 mm) of proximal section 812
because EM sensor 820 does not extend into distal section 814. The
pose of distal tip of section 814 can be determined using EM sensor
820 to measure or determine the global position and orientation of
a point along shape sensor 822 and using shape sensor 822 to
determine the shape of distal section 814 extending from the
measured point. The accuracy of shape sensor 822 can be relatively
high because shape sensor 822 only needs to measure the shape of a
relatively short section 814 of catheter 810, rather than the
entire length of catheter 810. For example, in one case, the
accuracy of the position measurement for the distal tip of section
814 is a function of the position and orientation accuracy of the
EM sensor 820 (typically about 1 mm and 0.01 radians respectively)
and the position accuracy of the shape sensor (0.15% of the length
of section 814). If 6-DoF EM sensor 820 is about 115 mm away from
the distal tip, the typical tip position accuracy would be about
2.5 mm.
FIG. 8B shows a catheter 830 that uses two 5-DoF EM sensors 840 and
841 in a proximal section 832 to measure six degrees of freedom of
a base point along a shape sensor 842 that extends into a distal
section 834 of catheter 830. Coils of EM sensors 840 and 841 are
within the same cross-section of proximal section 832 and therefore
are rigidly fixed relative to each other. EM sensors 840 and 841
can also contain sensing coils such as coils 720 and 730 having
wire loops with different orientations to measure different degrees
of freedom of a point along shape sensor 842. The roll angle can
thus be determined using the two measured pointing directions of
sensors 840 and 841 to define a reference frame. The use of 5-DoF
sensors 840 and 841 may allow a reduction in the diameter of
proximal section 832. In particular, 6-DoF EM sensors that are
available commercially generally have diameters that are larger
than the diameters of similar 5-DoF EM sensors. In accordance with
an aspect of the current invention, the diameter of a catheter may
be decreased through use of 5-DoF EM sensors. FIG. 9, for example,
illustrates how a distal section 832 of catheter 830 can
accommodate two 5-DoF EM sensors 840 and 841 and a main lumen 910
within a circular cross-sectional area that is smaller than the
area of distal section 812 of catheter 810. In particular, section
812 is larger because section 812 must accommodate the main lumen
and a 6-DoF sensor that has a larger diameter than do 5-DoF sensors
840 and 841.
FIG. 8C shows an embodiment of the invention using a sensor system
that may allow a proximal section 852 of catheter 850 to be even
smaller by using two 5-DoF EM sensors 860 and 861 that are
separated along the length of the proximal section 852.
Accordingly, only one 5-DoF EM sensor 860 or 861 needs to be
accommodated within the cross-section of proximal section 852.
However, since distal section 852 is flexible and may be bent when
in use, EM sensors 860 and 861 are not rigidly fixed relative to
each other, and a shape sensor 862 is used to measure the shape of
the portion of proximal section 852 between EM sensors 861 and 860
and the relative orientation of EM sensors 860 and 861. The shape
measurement between EM sensors 861 and 860 indicates the position
and orientation of sensor 860 relative to sensor 861, and the
relative configuration is needed for determination of a 6-DoF
measurement from the two 5-DoF measurement. Shape sensor 862 also
measures the shape of distal section 854, which indicates the
position and orientation of the distal tip relative to the global
position and orientation measurements determined using EM sensors
860 and 861.
FIG. 8D shows yet another catheter 870 using two 5-DoF EM sensors
880 and 881 that are separate along the length of catheter 870. The
sensing system in catheter 870 of FIG. 8D differs from the sensing
systems of FIGS. 8A, 8B, and 8C in that one EM sensor 880 is
located in a proximal section 872 of catheter 870 and the other EM
sensor 881 is located in a distal section 874 of catheter 870.
Accordingly, distal section 874 must be large enough to include
sensor 881, but still may allow a reduction in the diameter of
catheter 870 when compared to a catheter having a 6-DoF EM sensor
at a distal tip.
The use of two 5-DoF EM sensors in embodiments of FIGS. 8B, 8C, and
8D provides more information than is strictly required for a 6-DoF
measurement. In accordance with a further aspect of the invention,
one of the two 5-DoF EM sensors in catheter 830, 850, or 870 of
FIG. 8B, 8C, or 8D could be replaced with another type of sensor
that may not measure five degrees of freedom. For example, an
accelerometer could be employed in place of one of the two EM
sensors and provide a measurement of the direction of gravity,
i.e., down. Provided that the symmetry axis of the 5-DoF sensor is
not vertical, the combination of the measurements of a 5-DoF sensor
and a measurement of the orientation relative to the vertical
direction is sufficient to indicate measurements for six degrees of
freedom.
Although the invention has been described with reference to
particular embodiments, the description is only an example of the
invention's application and should not be taken as a limitation.
Various adaptations and combinations of features of the embodiments
disclosed are within the scope of the invention as defined by the
following claims.
* * * * *
References